Foamable compositions and formations treatment

ABSTRACT

Thermally stable foamable gelled compositions suitable for post-primary oil recovery, e.g., steam- or gas-foamed systems comprising water, a surfactant, a polymeric viscosifier, an aldehyde component, and at least one phenolic component such as resorcinol, catechol, and the like, as well as selected oxidized phenolic materials such as 1,4-benzoquinone of natural or syntheic origin and natural and modified tannins. The gel compositions can additionally contain gel stabilizers such as sulfomethylated quebracho (SMQ) and chemical buffering agents such as sodium bicarbonate.

This is a divisional application of my copending application having Ser.No. 100,085, filed Dec. 4, 1979, now U.S. Pat. No. 4,300,634.

This invention relates to gelled compositions and to displacing oil insubterranean formations. In accordance with one aspect, this inventionrelates to thermally stable foamable gelled compositions comprising asurfactant, a polymeric viscosifier, an aldehyde, and at least onephenolic component such as resorcinol, catechol, and the like, as wellas selected oxidized phenolic materials such as 1,4-benzoquinone ofnatural or synthetic origin and natural as well as modified tannins. Inaccordance with another aspect, this invention relates to foamablegelled compositions containing as surfactant, a polymeric viscosifier,and a gel stabilizer. In accordance with a further aspect, thisinvention relates to foamable gelled compositions containing asurfactant, a polymeric viscosifier, and a chemical buffering agent. Ina further aspect, this invention relates to foamed gelled compositionscontaining a surfactant and as polymeric viscosifiers a polyacrylamideor a cellulose polymer, an aldehyde, and a phenolic component with orwithout a gel stabilizer and a chemical buffering agent. In accordancewith a still further aspect, this invention relates to fluiddisplacement of oil within subterranean formations using theabove-described foamable gelled compositions in a steam- or gas-foamedsystem.

In oil well production, it is quite common to inject various gases,including steam, into oil wells to increase the production of oil fromthose wells. One common method of increasing production is the cyclicsteam stimulation method wherein production of oil from the well isperiodically interrupted and steam is injected in the well. Steam servesto melt some of the waxes in the strata and reduce the viscosity of theoil surrounding the wellbore so that it will flow more readily into thewellbore and be produced therefrom. A second method is the direct driveinjection of steam or other gases continuously into one well wherebyoils in the various earth strata are pushed ahead of the steam or gasbeing injected and are produced from another nearly well.

One of the problems faced in either type of injection of gases or steaminto the well arises from the varying permeability of the differentearth strata. Where there is a considerable difference in thepermeability of different strata, the injected gas will flow into themore permeable strata preferentially or, on occasion, almostexclusively. Since the oil to be produced may be very largely in theless permeable strata, a considerable quantity of gas or steam will beinjected into the well with little success.

Various methods of plugging or sealing off the highly permeable strataso that the steam may be directed into the less permeable strata havebeen proposed. One method which has been proposed is the introduction offoam into the more permeable strata by pumping into the well a watersolution of a surface-active agent. Another method involves introducingsteam and a foaming agent into the formation whereby a foam having steamas its gaseous phase is formed, and, upon condensation of the steam dueto loss of heat, the foam collapses. The present invention is directedto an improved process for increasing the resistance to fluid flow overa longer period of time when using steam and a foaming agent which foamshaving steam as its gaseous phase.

The present invention provides a solution for, or at least mitigates,the above-discussed problems. The present invention provides improvedmethods for steam diversion in subterranean formations as well as newfoamable gel compositions for use in said method.

Accordingly, an object of this invention is to provide for theproduction of oil from an oil-bearing formation or stratum.

It is another object of this invention to increase the efficiency of oilrecovery from such a formation.

Another object of this invention is to provide a method for sealingportions of a formation which have a relatively high permeability whichinterferes with the use of a driving force to force oil from lesspermeable portions of the formation.

A further object of this invention is to provide a higher pressure,e.g., steam direct drive system, for producing oil from an oil-bearingformation.

Another object of this invention is to provide a method for temporarilyplugging permeable strata.

It is a further object of this invention to provide a process forproducing a well by plugging more permeable strata with aself-destructive foam.

Other objects, aspects, and the several advantages of the invention willbecome apparent to those skilled in the art upon reading thespecification and the appended claims.

In accordance with the invention, gelled compositions are providedcomprising water; a surfactant; a water-dispersible polymer selectedfrom cellulose ethers, polyacrylamides, biopolysaccharides, andpolyalkylene oxides; one or more water-dispersible aldehydes; and one ormore phenolic components such as resorcinol, catechol, and the like, aswell as selected oxidized phenolic components such as 1,4-benzoquinoneof natural or synthetic origin and natural and modified tannins,optionally containing a gel stabilizer such as sulfomethylated quebracho(SMQ) and a chemical buffering agent such as sodium bicarbonate.

Further, in accordance with the invention, the above and other objectsof the invention are accomplished by injecting steam into subterraneanoil-bearing formations together with an aqueous surfactant solutioncontaining a chemically crosslinkable, water-dispersible polymer whichprevents the surfactant from foaming until after it is in the formationand after the polymer breaks down due to heat in the formation. Afterthe polymer breaks down, the surfactant forms a self-collapsing foamhaving a condensable gas as its gaseous phase.

More specifically, according to the invention, an aqueous surfactantsolution containing at least one chemically crosslinkable, at leastwater-dispersible polymer selected from polyacrylamides and relatedpolymers, cellulose ethers, polyalkylene oxides and polysaccharideswhich can be crosslinked or gelled in an aqueous medium withaldehyde/phenolic gelling agents are injected with steam intosubterranean oil-bearing formations under conditions which produce aselective blocking due to the formation of foam in the more permeablesections of the formation which forces injection steam to produce oilfrom less depleted portions of the formation.

In accordance with one specific embodiment, gelled cellulose etherpolymers and surfactants are injected with steam into a subterraneanoil-bearing formation through a well to divert the steam to the zonescontaining oil. The polymers prevent the surfactants from foaming untilthese materials are in the formation while serving to plug the moreporous zones until the polymers are broken down by heat.

In accordance with one presently preferred embodiment of the invention,an aqueous surfactant solution containing a gelled cellulose etherpolymer is injected with steam into a formation either through aninjection well or a production well to selectively plug or block themore depleted portions of the formation and thereby force the remainingsteam to produce oil from the less depleted portions of the formation.

As indicated hereinbefore, it is presently preferred to use gelledcellulose ether polymers in combination with foamable surfactants toreduce channeling in steam drive systems in subterranean oil-bearingformations. Other polymers and polysaccharides which can be crosslinkedor gelled in an aqueous medium can be used with and/or instead ofcellulose ether polymers to make the gels.

Further, in accordance with one specific embodiment of the invention,the foamable gelled polymer compositions defined above can additionallycontain a gel stabilizer and/or a chemical buffering agent.

In accordance with another specific embodiment of the invention, thecombination of formaldehyde and resorcinol added to a thickened aqueoussolution containing a water-dispersible polymer as defined results instable gels with temperature-dependent gelation rates.

Still further, in accordance with other broad aspects of the invention,there are provided methods for preparing the gelled compositions of theinvention.

In some embodiments of the invention, only one aldehyde can be used; ifdesired, however, a mixture of aldehydes can be used.

In some embodiments of the invention, only one phenolic compound can beused; if desired, however, a mixture of phenolic compounds can be used.

The invention compositions are suitable as gas or steam diversion agentsin oil well treatments. The gel foam of the invention can be used indirect steam drive applications, particularly where channeling problemsare observed between injection and production wells. The inventivecompositions can also be used in other thermal operations, particularlygas injection operations, i.e., flue gas, nitrogen, CO₂, where airchanneling problems through fractures or high permeability nonfracturedzones is a problem.

The polymeric materials which are suitable for use in the practice ofthe invention include at least one chemically crosslinkable, at leastwater-dispersible polymer selected from the group consisting ofpolyacrylamides and related polymers, cellulose ethers, polyalkyleneoxides, and polysaccharides which can be gelled in an aqueous mediumwith aldehyde and phenolic gelling agents. Where used, in thespecification and in the claims, unless otherwise specified, the term"polymer" is emloyed generically to include both homopolymers andcopolymers, and the term "water-dispersible polymers" is employed toinclude those polymers which are truly water-soluble and those which aredispersible in water or other aqueous medium to form stable colloidalsuspensions which can be crosslinked as described in U.S. Pat. No.3,785,437 and U.S. Pat. No. 3,373,810, which are incorporated herein byreference. Representative examples of suitable polymers, the preparationof these polymers, and specific polymeric materials that can be employedin the present invention are set forth in said patents.

As set forth in U.S. Pat. No. 3,785,437, representative cellulose etherswhich can be used in the practice of the present invention include,inter alia, the various carboxyalkyl cellulose ethers, e.g.,carboxyethyl cellulose and carboxymethyl cellulose (CMC); mixed etherssuch as carboxyalkyl hydroxyalkyl ethers, e.g., carboxymethylhydroxyethyl cellulose (CMHEC); hydroxyalkyl celluloses such ashydroxyethyl cellulose and hydroxypropyl cellulose; alkylhydroxyalkylcelluloses such as methylhydroxypropyl cellulose; alkyl celluloses suchas methyl cellulose, ethyl cellulose, and propyl cellulose;alkylcarboxyalkyl celluloses such as ethylcarboxymethyl cellulose,alkylalkyl celluloses such as methylethyl cellulose; andhydroxyalkylalkyl celluloses such as hydroxypropylmethyl cellulose; andthe like. Many of said cellulose ethers are available commercially invarious grades. Cellulose ethers are commonly designated in practice asCMC-7, CMC-9, CMC-12, etc., wherein the 7, 9, and 12 refer to a degreeof substitution of 0.7, 0.9, and 1.2, respectively.

Any suitable polymer of acrylamide meeting the above-statedcompatibility requirements can be used in the practice of the invention.Thus, under proper conditions of use, such polymers can include variouspolyacrylamides and related polymers which are water-dispersible andwhich can be used in an aqueous medium, with the gelling agentsdescribed herein, to give an aqueous gel as set forth in U.S. Pat. No.3,785,437. These can include the various substantially linearhomopolymers and copolymers of acrylamide and methacrylamide. Bysubstantially linear is meant that the polymers are substantially freeof crosslinking between the polymer chains. Said polymers can have up toabout 45, preferably up to about 40, percent of the carboxamide groupshydrolyzed to carboxyl groups. Generally speaking, as the degree ofhydrolysis increases, the polymers tend to become more difficult todisperse in brines, especially hard brines. Thus, one presently morepreferred group of polymers includes those wherein not more than about20 percent of the carboxamide groups are hydrolyzed. As used herein andin the claims, unless otherwise specified, the term "hydrolyzed"includes modified polymers wherein the carboxyl groups are in the acidform and also such polymers wherein the carboxyl groups are in the saltform, provided said salts are water-dispersible. Such salts include theammonium salts, the alkali metal salts, and others which arewater-dispersible. Hydrolysis can be carried out in any suitablefashion, for example, by heating an aqueous solution of the polymer witha suitable amount of sodium hydroxide.

All the polymers useful in the practice of the invention arecharacterized by high molecular weight. The molecular weight is notcritical so long as the polymer has the above-describedwater-dispersible properties and meets the above-stated compatabilityrequirements. It is preferred that the acrylamide-derived polymers havea molecular weight of at least 500,000, more preferably at least about2,000,000, whereas the suitable cellulose ether polymers should have amolecular weight of at least 200,000. The upper limit of molecularweight is unimportant so long as the polymer is water-dispersible andthe gelled composition therefrom can be pumped. Thus, it is within thescope of the invention to use polymers having molecular weights as highas 20,000,000 or higher and meeting said conditions.

The amount of the above-described polymers used in preparing the gelledcompositions of the invention can vary widely depending upon theparticular polymer used, the purity of said polymer, and propertiesdesired in said compositions. In general, the amount of polymer usedwill be a water-thickening amount, i.e., at least an amount which willsignificantly thicken the water to which it is added. For example,amounts in the order of 25 to 100 parts per million by weight (0.0025 to0.01 weight percent) have been found to significantly thicken water.Generally speaking, amounts of the above-described polymers in the rangeof from 0.1 to 5, preferably from 0.3 to about 2, weight percent, basedon the total weight of the composition, can be used in preparing gelledcompositions for use in the practice of the invention.

As a further guide, when the polymer used is one of the AMPS or AMPSsalt copolymers containing 50 mol percent or more AMPS or AMPS saltunits, the polymer concentration will preferably be in the range of from0.6 to 3, more preferably 0.75 to about 2, weight percent, based on thetotal weight of the composition. Similarly, when the polymer used is apartially hydrolyzed polyacrylamide or polymethacrylamide, or one of theMTMMS or DEMMS copolymers (see U.S. Pat. No. 4,103,742), the polymerconcentration will preferably be in the range of from 0.75 to about 2weight percent, based on the total weight of the composition. Ingeneral, with the proper amounts of phenolic compound and aldehyde, theamount of polymer used will determine the consistency of the gelobtained. Small amounts of polymer will usually produce liquid mobilegels which can be readily pumped. Large amounts of polymer will usuallyproduce thicker, more viscous, somewhat elastic gels. Gels having aviscosity "too thick to measure" by conventional methods can still beused in the practice of the invention. Thus, there is really no fixedupper limit on the amount of polymer which can be used as long as thegelled composition can be pumped in accordance with the methods of theinvention.

Other polymers that can be used in the gels of the invention includepolyalkylene oxides and biopolysaccharides, which are biochemicallysynthesized polysaccharides. These polymers are well known and can beproduced in accordance with known procedures. Suitable polyalkyleneoxides that can be used include polyethylene oxide, polypropylene oxide,polybutylene oxide and the like as well as derivatives thereof as setforth in U.S. Pat. No. 4,124,073, issued to Donald R. Wier on Nov. 7,1978, which is incorporated herein by reference. Preparation details ofthe biopolysaccharides can be found in U.S. Pat. No. 3,373,810, which isincorporated herein by reference, and references cited therein. Theamounts of these polymers used in the instant gel compositions can bethe same as for the acrylamide polymers and cellulose ethers.

Any suitable water-dispersible aldehyde meeting the above-statedcompatibility requirements can be used in the practice of the invention.Thus, under proper conditions of use, both aliphatic and aromaticmonoaldehydes, and also dialdehydes, can be used. The aliphaticmonoaldehydes containing from one to about 10 carbon atoms per moleculeare presently preferred. Representative examples of such aldehydesinclude formaldehyde, paraformaldehyde, acetaldehyde, propionaldehyde,butyraldehyde, isobutyraldehyde, valeraldehyde, heptaldehyde, decanal,and the like. Representative examples of dialdehydes include glyoxal,glutaraldehyde, terephthalate, and the like. Various mixtures of saidaldehydes can also be used in the practice of the invention. The term"water-dispersible" is employed generically herein to include both thosealdehydes which are truly water-soluble and those aldehydes of limitedwater solubility but which are dispersible in water or other aqueousmedia to be effective gelling agents. Formaldehyde is the preferredaldehyde compound for use in the present invention.

Any suitable water-dispersible phenol or naphthol meeting thecompatibility requirements set forth above can be used in the practiceof the invention. Suitable phenols include monohydroxy and polyhydroxynaphthols. Phenolic compounds suitable for use in the present inventioninclude phenol, catechol, resorcinol, phloroglucinol, pyrogallol,4,4'-diphenol, 1,3-dihydroxynaphthalene, and the like. Other phenoliccomponents that can be used include at least one member of selectedoxidized phenolic materials of natural or synthetic origin such as1,4-benzoquinone; hydroquinone or quinhydrone; as well as a natural ormodified tannin such as quebracho or sulfomethylated quebrachopossessing a degree of sulfomethylation (DSM) up to about 50. (See U.S.Pat. No. 3,344,063, col. 3, lines 15-32, which is incorporated herein byreference.) The DMS of sulfomethylated quebracho (SMQ) is sometimesindicated by writing, for example, SMQ 50 for SMQ having a DSM of 50.Resorcinol and catechol are the preferred phenolic compounds for use inthe present invention for most water diversion applications.Phloroglucinol gives a very fast gelation rate and is preferred for someapplications.

Any suitable amount of aldehydes and phenolic compounds can be used inthe practice of the invention. In all instances the amounts of aldehydeand phenolic compound used will be a small, but effective amount whichis sufficient to cause gelation of an aqueous dispersion of the polymer,the aldehyde, and the phenolic compound. As a general guide, the amountof aldehyde used in preparing the gelled compositions of the inventionwill be in the range of from about 0.02 to 2, preferably 0.1 to about0.8, weight percent, based on the total weight of the composition. Theweight ratio of sulfomethylated quebracho to polymer is in the range of0.1:1 to 5:1, preferably 0.5:1 to 2:1. The polymer concentration is inthe broad range of 1,000 to 50,000 ppm, preferably 3,000 to 20,000 ppm.The concentration of phenolic material (other than SMQ) will be in therange of 0.005 to 2, preferably 0.04 to 1, weight percent.

As indicated previously, it is also within the scope of the invention touse gel stabilizers such as sulfomethylated quebracho. Quebracho is aflavotannin which is water-extracted from the bark and wood of thequebracho tree. The conventional method of preparing quebracho is todisintegrate the wood and bark followed by extraction with water. Theaqueous extract is concentrated to remove about 85 percent of the water,and the residual quebracho is spray-dried. Quebracho is the commercialcatechol tannin, or flavotannin product. The quebracho can besulfomethylated as is known in the art, as is disclosed in U.S. Pat. No.3,344,063. The amount of gel stabilizer used will vary from about 20 toabout 200 weight percent, based on the weight of polymer. When used as agel stabilizer, the sulfomethylated quebracho will have a DSM in thebroad range of about 85 to 250, preferably about 100 to about 200.

It is also within the scope of the invention to use a chemical bufferingagent during the gelation process. Most preferred buffering agentsinclude water-soluble bicarbonate salts such as NaHCO₃, KHCO₃, andLiHCO₃. The corresponding carbonate salts are also suitable. The amountof chemical buffering agent used will vary broadly from about 0.05 toabout 1, preferably about 0.1 to about 0.5, weight percent, based on theweight of the total composition.

As indicated hereinbefore, the objects of the invention are achieved inselectively blocking and plugging permeable sections of subterraneanoil-bearing formations by injecting with steam an aqueous surfactantsolution containing a water-dispersible polymer which prevents thesurfactant from foaming until it has been in the formation for sometime. The amount of surfactant present in the aqueous solution should besufficient to form a stable, self-collapsing foam when said solution iscontacted with steam after the polymer has broken down due to heat.Generally, the aqueous solution will contain about 0.1 to about 3 weightpercent polymer. The amount of surfactant present in the solution willordinarily be in the range of about 0.1 to about 10 weight percent,preferably 1 percent to 6 percent, based on the weight of the totalcomposition.

Various types of surface-active agents can be used in the process of myinvention, either nonionic, anionic, or cationic and mixtures thereof.Commercial surface-active agents of the alkylphenoxy polyethoxy ethanolclass and commonly available household cleansers have been tested andfound satisfactory in the practice of my invention. The surfactants mustbe stable at the operating conditions of this invention. For example,Trend detergent, manufactured by Purex Corporation, Ltd., has provedsatisfactory, as well as other household cleaning compounds, hand andlaundry soaps, and rug shampoos.

Other water-soluble surfactants which have been found stable attemperatures used to carry out this invention arealkylphenoxypoly(ethyleneoxy) ethanol surfactants sold by GAFcorporation, Chemical Division, 140 West 51st, New York, N.Y. 10020, asIgepal surfactants. The particular Igepal surfactants are sold under thetrade names as DM970, DM730, DM710, and CA720. The aliphatic polyethersurfactants sold by the GAF corporation under the trade names AntaraxBL330 and BL344 have also been found to be effective water-solublesurfactants usable in carrying out this invention.

Surfactants have been used to produce foams in formations. Society ofPetroleum Engineers Journal, December 1970: S. H. Raza, "Foam in PorousMedia: Characteristics and Potential Applications." Note FIG. 2 andpages 330 and 335. A surfactant solution useful in the present inventionis OK liquid (ammonium lauryl sulfate plus amide builder manufactured byProctor and Gamble) in a water solution at a concentration as low asapproximately 0.3 weight percent. Such solutions are referred to in theSociety of Petroleum Engineers Journal as useful to produce foam inporous media. After the injection of the surfactant solution into theproducing well, steam channeling through the introduced solution toreach the producing well will generate a foam consisting of water as theexternal phase and steam as the gaseous phase. This foam is generated inprecisely the porosities through which the undesirable channeling hasoccurred and therefore a selective blocking is produced forcing theremaining steam to produce oil from less depleted portions of theformation.

The aqueous surfactant solution containing the gelled polymer can beintroduced into the formation along with steam either through aninjection well penetrating the formation and/or a production wellpenetrating the formation.

The invention is applicable to formations produced by direct steam driveas where there is a steam injection well and a producing well. It isalso applicable to the production of a formation using a cyclic or"huff-puff" operation. In any event, when there is being produced fromthe producing well or during a producing cycle excessive steam and/orhot water, the invention can be applied to substantially plug or sealchannelings through which the steam preferentially finds its way,resulting in a production of insufficient oil.

Any suitable method can be employed for preparing the gelledcompositions of the invention. Thus, any suitable mixing technique ororder of addition of the components of said composition to each othercan be employed which will provide a composition having sufficientstability to degeneration by the heat of the formation (in which thecomposition is to be used) to permit good penetration of the compositioninto said formation. However, it is ordinarily preferred to firstdissolve or disperse the polymer in water before contacting the polymerwith the other components. The mixing order can vary with the type ofpolymer used. Some suitable mixing orders, with the components named inorder of mixing, include: water--surfactant--polymer--phenoliccompound--aldehyde; water--phenoliccompound--surfactant--polymer--aldehyde; phenoliccompound--polymer--water--surfactant--aldehyde; andwater--surfactant--polymer--aldehyde--phenolic compound; and the like.It is within the scope of the invention to moisten or slurry the polymerwith a small amount, e.g., about 1 to about 6 weight percent, based onthe weight of the polymer, of a small amount of a low molecular weightalcohol, e.g., C₁ to C₃ alcohols, as a dispersion aid prior todispersing the polymer in water.

The gelled or ungelled compositions of the invention can be prepared onthe surface in a suitable tank equipped with suitable mixing means, andthen pumped down the well and into the formation employing conventionalequipment for pumping gelled compositions. However, it is within thescope of the invention to prepare said compositions while they are beingpumped down the well. This technique is sometimes referred to as "on thefly." For example, a solution of the polymer in water can be prepared ina tank adjacent the wellhead. Pumping of this solution through a conduitto the wellhead can then be started. Then, a few feet downstream fromthe tank a suitable connection can be provided for introducing eitherthe phenolic compound or the aldehyde and surfactant into said conduit,preferably as an aqueous solution. Then, a few feet farther downstreamthe other of said phenolic or aldehyde and surfactant components can besimilarly introduced. As will be understood by those skilled in the art,the rate of introduction of said components into said conduit willdepend upon the pumping rate of the polymer solution through saidconduit. Any of the above-mentioned orders of addition can be employedin said "on the fly" technique. Mixing orifices can be provided in saidconduit, if desired.

It is within the scope of the invention to precede the injection of thegelled composition into the well and out into the formation with apreflush of a suitable cooling fluid, e.g., water. Such fluids serve tocool the well tubing and formation and extend the useful operatingtemperature range of said compositions. The volume of said cooling fluidso injected can be any suitable volume sufficient to significantlydecrease the temperature of the formation being treated, and can varydepending upon the characteristics of the formation. For example,amounts up to 20,000 gallons or more can be used to obtain a temperaturedecrease in the order of 100° to 250° F.

The following example will serve to further illustrate the invention,but should not be considered as unduly limiting on the invention.

SPECIFIC EXAMPLE

Two solutions of aqueous polyacrylamide (10,000 ppm Reten 420, acommercially available acrylamide homopolymer with a 6.3 percent degreeof hydrolysis) were prepared by stirring the appropriate weight ofpolymer in 200 ml aliquots of tap water for a few minutes and thenrolling the individual mixtures in sealed containers for several hoursto complete solution. To these respective polymer solutions were addedthe listed components in the order given:

    ______________________________________                                        Formulation A (Control)                                                                         Formulation B (Invention)                                   ______________________________________                                        (i)  Resorcinol (2000 ppm)                                                                          (i)    Resorcinol (2000 ppm)                            (ii) NaHCO.sub.3 (2000 ppm)                                                                         (ii)   NaHCO.sub.3 (2000 ppm)                           (iii)                                                                              Formaldehyde (2000 ppm)                                                                        (iii)  Formaldehyde                                                                  (2000 ppm)                                                             (iv)   Cor 180.sup.a Surfactant                                                      (3% by volume)                                   ______________________________________                                         .sup.a A description of Cor 180 is given in U.S. Pat. No. 3,993,133 at        Col. 8.                                                                  

During the addition of the various components, the polymer solutionswere stirred with a Hamilton Beach Maltmixer. Formulations A and B weretransferred to individual glass pressure bottles and the sealed vesselswere aged in an oil bath at 325° F. After 12 days at 325° F., both gelsfrom formulations A and B were stable, however, it was noticed that theinventive formulation exhibited a slower gelation rate. This observedthermal stability of the gel resulting from the inventive formulation Bsubstantiates the feasibility of using the instant composition tostabilize foams used at high temperatures for selectively pluggingoil-bearing subterranean formations.

Although the invention has been expressed in terms of use in steam drivetreatment of subterranean formations, it is also within the scope of theinvention to use other gases such as flue gas, nitrogen, CO₂ and thelike. These can be used under high temperature as well as lowtemperature treatment processes.

I claim:
 1. A foamable gelled composition consisting essentially of(a)water, (b) a water-soluble surfactant in an amount which is sufficientto form a stable, self-collapsing foam when the composition is contactedwith steam after polymer component (c) breaks down due to heat, (c) awater-thickening amount of a water-dispersible polymer selected from thegroup consisting of cellulose ethers, polyacrylamides, polyalkyleneoxides, and biopolysaccharides produced by the action of bacteria of thegenus Xanthomonas upon carbohydrates, (d) a small, but effective amountin the range of 0.02 to 2 weight percent, of at least one aldehydecomponent selected from the group consisting of glyoxal, glutaraldehyde,and terephthaldehyde, and aliphatic monoaldehydes having from one toabout 10 carbon atoms per molecule, and (e) a small, but effectiveamount in the range of 0.005 to 2 weight percent of at least onephenolic compound selected from the group consisting of phenol,catechol, resorcinol, phloroglucinol, pyrogallol, 4,4'-diphenol,2,3-dihydroxynaphthalene, 1,4-benzoquinone, hydroquinone, quinhydrone,and quebracho which amounts of aldehyde (d) and phenolic compound (e)are sufficient to cause gelation of an aqueous dispersion of polymer (c)and form said gelled composition.
 2. A composition according to claim 1wherein aldehyde (d) is formaldehyde.
 3. A composition according toclaim 1 wherein the amount of (b) present ranges from about 0.1 to about10 weight percent based on the weight of the total composition.
 4. Acomposition according to claim 1 wherein there is additionallypresent(f) a gel stabilizer comprising sulfomethylated quebracho havinga DSM ranging from about 85 to 250 in an amount ranging from about 20 toabout 200 weight percent based upon the weight of polymer (c) and (g) achemical buffering agent comprising water-soluble carbonate andbicarbonate salts in an amount ranging from 0.05 to 1 weight percentbased on the weight of total composition.
 5. A composition according toclaim 4 where (g) is sodium bicarbonate.
 6. A composition according toclaim 1 wherein the amount of (b) is in the range of 1 to 6 weightpercent, the amount of (c) is in the range of 0.1 to 5 weight percent,the amount of (d) is in the range of 0.1 to 0.8 weight percent, and theamount of (e) is in the range of 0.04 to 1 weight percent.
 7. Acomposition according to claim 6 wherein (c) is a partially hydrolyzedpolyacrylamide or a cellulose ether, (d) is formaldehyde, and (e) isphenol, catechol, hydroquinone, 1,4-benzoquinone, quebracho,sulfomethylated quebracho having a DSM of 10-50, resorcinol, orphloroglucinol.
 8. A composition according to claim 1 wherein (c) is apartially hydrolyzed polyacrylamide wherein not more than about 45percent of the carboxamide groups are initially hydrolyzed to carboxylgroups; (d) is formaldehyde, and (e) is resorcinol.
 9. A compositionaccording to claim 8 which additionally contains(f) sulfomethylatedquebracho (SMQ) having a DSM ranging from about 85 to 250 as a gelstabilizer and/or (g) sodium bicarbonate as a chemical buffering agent.